Outer membrane lipoprotein spanin subunit (o-spanin) encoded entirely within the +1 reading frame of the Rz gene. Following cleavage of its 19-residue signal peptide by signal peptidase II and lipid modification at Cys-20, the mature 40-residue proline-rich Rz1 lipoprotein is anchored to the inner leaflet of the Escherichia coli outer membrane, where it forms a disulfide-linked homodimer via Cys-29 and binds the C-terminal periplasmic domain of the inner membrane subunit Rz (i-spanin). Once endolysin R degrades the periplasmic peptidoglycan meshwork, the periplasm-spanning Rz-Rz1 complex oligomerizes and mediates fusion of the inner and outer membranes, rupturing the host outer membrane for progeny phage release.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0019076 viral release from host cell | IDA PMID:28040784 Genetic Analysis of the Lambda Spanins Rz and Rz1: Identific... | MODIFY | Summary: Mutational dissection of Rz1 demonstrates its requirement for spanin-mediated outer membrane disruption during phage lysis; refine to the more specific term GO:0090680. Reason: GO:0019076 (viral release from host cell) is a broad parent term; PMID:28040784 specifically assays spanin-mediated outer membrane disruption during cytolytic phage lysis, which is captured by the descendant term GO:0090680 (viral release via disruption of host outer membrane) already annotated to Rz1. Proposed replacements: viral release via disruption of host outer membrane Supporting Evidence: PMID:28040784 Coliphage lambda proteins Rz and Rz1 are the inner membrane and outer membrane subunits of the spanin complex-a heterotetramer that bridges the periplasm and is essential for the disruption of the outer membrane during phage lysis. |
| GO:0020002 host cell plasma membrane | EXP PMID:23387988 Spanin function requires subunit homodimerization through in... | MODIFY | Summary: Rz1 is the outer membrane lipoprotein subunit (o-spanin), whereas Rz is the inner (plasma) membrane subunit; replace GO:0020002 with GO:0039662 (host cell outer membrane). Reason: Rz1 is localized to the inner leaflet of the Escherichia coli outer membrane (GO:0039662), not the host inner/plasma membrane (GO:0020002). PMID:23387988 explicitly identifies Rz1 as the outer membrane spanin (o-spanin). Proposed replacements: host cell outer membrane Supporting Evidence: PMID:23387988 Rz, the inner membrane or i-spanin, has a largely alpha-helical periplasmic domain, whereas Rz1, the outer membrane or o-spanin, has a 25% proline content with no predicted secondary structure. |
| GO:0020002 host cell plasma membrane | IEA GO_REF:0000044 | MODIFY | Summary: Coarse mapping from UniProt subcellular location SL-0376 (Host cell outer membrane) to host cell plasma membrane; should be replaced with the exact term GO:0039662 (host cell outer membrane). Reason: UniProtKB-SubCell:SL-0376 denotes 'Host cell outer membrane' in Rz1-uniprot.txt, and experimental fractionation (PMID:8626053, PMID:18713319) proves Rz1 is an outer membrane lipoprotein. Replacing GO:0020002 with GO:0039662 corrects the compartment to the host outer membrane. Proposed replacements: host cell outer membrane Supporting Evidence: file:LAMBD/Rz1/Rz1-uniprot.txt SUBCELLULAR LOCATION: Host cell outer membrane {ECO:0000269|PubMed:18713319, ECO:0000269|PubMed:23387988} |
| GO:0031640 killing of cells of another organism | IEA GO_REF:0000043 | MODIFY | Summary: Overly general keyword-mapped term from KW-0204 (Cytolysis); should be refined to GO:0090680 and GO:0044659. Reason: GO:0031640 is an overly broad inter-organismal killing term; the specific descendant viral lysis terms GO:0090680 (viral release via disruption of host outer membrane) and GO:0044659 (viral release from host cell by cytolysis) are already annotated to Rz1. Proposed replacements: viral release via disruption of host outer membrane viral release from host cell by cytolysis Supporting Evidence: file:LAMBD/Rz1/Rz1-uniprot.txt Component of the spanin complex that disrupts the host outer membrane and participates in cell lysis during virus exit (PubMed:22904283, PubMed:23387988, PubMed:25870259). |
| GO:0039662 host cell outer membrane | IDA PMID:8626053 The Rz1 gene product of bacteriophage lambda is a lipoprotei... | ACCEPT | Summary: Membrane fractionation and palmitate labeling in induced Escherichia coli lambda lysogens demonstrate that Rz1 is a lipoprotein localized almost exclusively in the host outer membrane. Reason: Direct biochemical evidence establishing that mature Rz1 is anchored in the Escherichia coli outer membrane. Supporting Evidence: PMID:8626053 In induced Escherichia coli lambda lysogens Rz1 was found almost exclusively in the outer membrane (OM). |
| GO:0044659 viral release from host cell by cytolysis | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-based annotation to viral release from host cell by cytolysis accurately reflects Rz1's essential role in the lambda three-step host lysis pathway. Reason: Consistent with genetic and physiological evidence showing that Rz1 is required for cytolytic host cell lysis (PMID:22904283). Supporting Evidence: file:LAMBD/Rz1/Rz1-uniprot.txt Component of the spanin complex that disrupts the host outer membrane and participates in cell lysis during virus exit (PubMed:22904283, PubMed:23387988, PubMed:25870259). |
| GO:0045861 negative regulation of proteolysis | IDA PMID:20734329 The lambda spanin components Rz and Rz1 undergo tertiary and... | REMOVE | Summary: In PMID:20734329, heterodimerization of Rz1 with Rz folds the C-terminal periplasmic domain of Rz and sterically shields it from degradation by endogenous periplasmic proteases; Rz1 does not function as a regulator of proteolysis. Reason: Over-annotation of a structural complex-assembly effect. Rz1 is the outer membrane subunit of the Rz-Rz1 spanin complex, not a protease inhibitor or regulator of proteolytic pathways; protection of its binding partner Rz from periplasmic proteolysis is a consequence of quaternary complex formation and disorder-to-helix folding. Supporting Evidence: PMID:20734329 The results indicate that in vivo , Rz1 protects the C-terminal domain of Rz from proteolysis by forming a complex that spans the entire periplasm through the meshwork of the intact PG. |
| GO:0061025 membrane fusion | IDA PMID:25870259 Membrane fusion during phage lysis. | ACCEPT | Summary: Spheroplast fusion assays demonstrate that the lambda Rz-Rz1 spanin complex directly mediates fusion between the Escherichia coli inner and outer membranes during lysis. Reason: Direct experimental demonstration that Rz1, in complex with Rz, drives inner-outer membrane fusion after peptidoglycan degradation. Supporting Evidence: PMID:25870259 Here we show that the spanins of the paradigm coliphage lambda mediate efficient membrane fusion. This supports the notion that the last step of lysis is the fusion of the IM and OM. |
| GO:0090680 viral release via disruption of host outer membrane | IMP PMID:22904283 The spanin complex is essential for lambda lysis. | ACCEPT | Summary: Null mutations in Rz1 prevent outer membrane rupture during prophage induction, arresting cells in a spherical form bounded by an intact outer membrane. Reason: Core biological process of the Rz1 o-spanin subunit in complex with Rz. Supporting Evidence: PMID:22904283 In both cases, lysis failed to occur in inductions of isogenic prophages carrying null mutations in the spanin genes. In both systems, instead of an envelope rupture, the induced cells were converted from a rod shape to a spherical form. |
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Download this section (compressed HTML)Q: How does the central polyproline motif of mature Rz1 promote outer membrane curvature or lipid bilayer destabilization during the post-peptidoglycan-cleavage fusion step?
Q: What is the structural basis by which a single covalent disulfide bond in either the Rz homodimer or the Rz1 homodimer suffices to support spanin-mediated membrane fusion?
Experiment: Use solution NMR and EPR spectroscopy of lipid-anchored Rz1 in outer-membrane-mimetic nanodiscs to determine how the proline-rich region interacts with the phospholipid headgroups before and after sRz binding.
Experiment: Perform site-specific photo-cross-linking across the C-terminal residues of Rz1 (residues 50-60) in vivo to map the exact contact residues on Rz CC2.
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